explicitly use bash interpreter

The tests use bash language features like 'let', which aren't supported
by /bin/sh on systems that use a conservative shell like dash.  This
patch changes the interpreter to /bin/bash.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
30 files changed